Kevin in Atlanta

Kevin Wilson's GTS is under the knife at Pete DeJong's in SC. This was after we got some pretty horrible compression numbers chasing high oil consumption to and from Frenzy.

Quit compression test when we saw 3 and 4 results because I knew it was coming apart.

So, the question is why two oil rings were worn to nothing and where are the springs that should be in the groves? ( I think we all know the answer to that question. )

I believe there no ZDDP in the oil for most of it's life.


Compression numbers

2 rings worn flat - Cylinder 3 and 4 on the bottom


Here's a couple of pictures of the tops of the pistons. Just a little carbon build up. Yikes!

ROG100

The cars ignition was so retarded I am amazed it ran. Jim Mayzurk's GTS was just the same carbon wise..

Mrmerlin

its melting as as it runs,
the rear cylinders run a lot hotter than the front ones do because the head gaskets have deteriorated ,
and dont have the flow restrictions like the new ones do.

SteveG

Anybody know if a borescope is useful for something like this? And if so, what would be minimum quality borescope to buy?

SwayBar

Kevin, thanks for sharing the pictures of the piston tops - I had no idea GTS pistons would look THAT bad!

GregBBRD

All GTS pistons that have not been modified look like that!

That ring wear is from something very abrasive being run through the engine. (The rings are soft.)

You can figure out what that abrasive was, but I can almost guarantee the intake was "done" not long ago.

The fun has just begun! Wait until the cylinder to wall clearance is measured! It will need new pistons and need to be bored oversize....
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Of course, Porsche has no inventory on 100.5mm GTS pistons....so it gets really complex, really fast.

Mrmerlin

Greg How about making a stroker with new parts ?
Is the answer Money?

Kevin in Atlanta

Let's wait until Pete measures the cylinders. All the pistons have been measured and are within spec.

GregBBRD

928 engines are just starting to wear out...they are now getting enough miles on them to need oversize pistons. Combine that with idiots not cleaning repainted (or powder coated) intake manifolds enough and suddenly, I need oversize pistons...lots of them.

Porsche currently has neither oversize '85/'86 pistons, nor oversize GTS pistons, which is making my job WAY more difficult.

But it does open the door to make "oversize" engines....
And you are correct. A "proper" 928 rebuild isn't cheap. An "oversize" version obviously costs more...so money becomes part of the equation.


I delivered a 5.8 liter GTS, today. The end product is way better of an engine than one would expect from the simple addition of 400cc's of volume. I suspect that the longer rod (I use significantly longer rods in these engines) which reduces the rod angle to the crankshaft, has some positive effect. A couple of tricks, here and there, combined with hundreds of hours of tuning these big engines makes the end result way smoother, through the entire power range, than any stock GTS ever dreamed of being, while dramatically increasing cruising fuel ecconomy.

The increased torque makes these engines sneaky fast. They remind me of driving a 993 Turbo....you "row" easily through the gears, short shifting....and you look down to see you're suddenly doing over 100mph...without trying.

They are, even under my very critical scrutiny, extremely impressive engines. (People think I'm really "critical" about what other people do....in reality, I'm 10x more critical of my own stuff! Very simply, nothing we do leaves my shop, until I'm 110% happy.)

Not much doubt, in my mind, that this would have been Porsche's 1998 928, if they had built it.
.

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Rob Edwards

Got a ride in this 5.8, it's a hoot. The midrange punch is really addictive!

RKD in OKC

My 94 GTS, 68K miles was using a quart every tank of gas. Just starting to get to the point of oil fouling plugs.
No oil in the intake
The piston tops did not have build up. Both the pistons and bores were in spec so only needed new rings.
The oil relief holes in the oil scraper ring groove were NOT drilled.
Drilled 4 holes where the flats were inside each piston, new rings, runs great and no oil usage.
Did new bearings while bottom end was apart. Were just starting to show a little brass.

Jim M.

Yes, my piston tops were the same. But I always had good oil pressure during normal driving and acceptable oil consumption for a GTS. During our 110F summers the oil pressure was low when idling in traffic, but 20W50 solved that.

blau928

This engine used to have pistons looking a little like those pictured in this post.....

Mark Anderson

We have the following in stock
928-103-042-64 100.5 3 pieces
928-103-042-65 100.5 1 piece
$195 each

ROG100

Greg - you need a better parts supplier 8>) - Porsche has 8 sitting in Germany 928 103 042 75. 100.5mm